Preparation of water from flue gases

ABSTRACT

An apparatus for preparing water from water-containing gases released in a conversion device for converting chemical energy into mechanical energy, comprising: at least one membrane which is adapted to at least partly allow passage of water molecules and substantially prevent passage of other molecules; a passage for guiding the waste gases along a first side of the membrane, a discharge pipe arranged on the second side of the membrane for discharging the water released on the second side of the membrane. The conversion device for converting chemical energy into mechanical energy is formed by a conversion device with external combustion, and the discharge pipe are formed at least partly by auxiliary equipment associated with the conversion device with external combustion.

The present invention relates to the preparation of low-salt, low-TOCand perhaps low-gas water, in particular water of high quality.

In a large number of countries in the world there exists a shortage ofpotable water. This is particularly the case in dry regions and inregions where the infrastructure for careful preparation and transportof potable water is inadequate.

It is therefore generally important to manage potable water aseconomically as possible and to utilize possible potable water sourcesas well as possible.

The currently most used sources of potable water are groundwater, springwater and surface water which, after purification, can be used aspotable water. In some cases rainwater is also used.

The object of the present invention is to provide means for thepreparation of water from sources which until now have not been used.The attempt is hereby made to provide water of a high purity which canbe used directly as boiler feed water or for other technicalapplications. The usual sources of potable water need hereby no longerbe drawn upon for this use.

The attempt is further made to provide such a apparatus wherein effortsin respect of investment, energy consumption and other effort areminimal.

Known from EP-A-O 192 893 is a preparation apparatus for preparing waterfrom water-containing gases released in a device for converting chemicalenergy into mechanical energy, wherein the preparation apparatuscomprises:

at least one membrane which is adapted to at least partly allow passageof water molecules and substantially prevent passage of other molecules;

means for guiding the gases containing water vapour along a first sideof the membrane,

discharge means arranged on the second side of the membrane fordischarging the water released on the second side of the membrane.

This prior art publication relates to a conversion device with internalcombustion. Such devices are used in large numbers in the form ofcombustion engines, both stationary and mobile. Heavy and bulkyauxiliary equipment is required to prepare water from the exhaust gasesof such a motor. A vacuum pump must thus be used to maintain asufficiently low pressure on the second side of the membrane and acondenser must be used to allow a sufficiently low temperature toprevail on the second side of the membrane.

These are costly, heavy and bulky apparatuses which it is hardlypossible to accommodate in a vehicle, certainly when provisions must bemade for storage of the prepared water. This is already in no wayproportional with the thus obtained yield of water. These drawbacks arealso relevant in respect of stationary engines.

The object of the invention is to provide an application of such apreparation apparatus in a situation in which these drawbacks do notoccur.

This object is achieved by such a preparation apparatus which ischaracterized in that the conversion device for converting chemicalenergy into mechanical energy is formed by a conversion device withexternal combustion, and in that the discharge means are formed at leastpartly by auxiliary equipment associated with the conversion device withexternal combustion.

These measures enable the use of the auxiliary equipment required in aconversion device for chemical energy to mechanical energy with externalcombustion. The external combustion supposes a Carnot cycle throughwhich an auxiliary medium must progress as energy carrier. Theprogression through a Carnot cycle requires the presence of a condenser.A pump is usually present to cause an underpressure to prevail in thecondenser.

The measures according to the invention enable the fruitful use of thesefacilities, so that these per se bulky appliances do not have to beplaced separately.

It is thus possible to use a heretofore unused source of water of a highquality, i.e. gases containing water vapour, such as the waste gases ofan energy conversion device. It is noted here that in the presentlyproposed use the prepared water is used as boiler feed water or as waterfor other industrial applications. This is the consequence of the highpurity of the water attainable with the apparatus according to theinvention. It is conceivable to use the water as potable water, i.e.after the addition of substances normally present in potable water, orby using membranes which allow through the substances in question.

According to a first embodiment the conversion device forms part of anelectric power station.

A conversion device of exceptionally large dimensions is present herewith a high rate of water-containing gas flows. The auxiliary equipmentis moreover of corresponding dimensions, so that the additional load bythe flow of the water preparation according to the invention has no orhardly any effect on the dimensioning of the auxiliary equipment. It isusually even possible to use this auxiliary equipment withoutmodifications, so that it is easy to arrange such a water preparationapparatus in an existing power station.

In view of the exceptionally large quantities of flue gases which areproduced by an electric power station, it is particularly attractive touse the flue gases as a source of water. As stated above, this resultsin large saving.

According to another embodiment the auxiliary equipment comprises acondenser and the discharge means re formed at least partly by thecondenser associated with the auxiliary equipment.

According to a further embodiment the condenser is connected to a pumpfor maintaining a pressure in the condenser which is lower than theambient pressure.

These measures also result in an effective use of components alreadypresent.

According to another preferred embodiment the membrane is only suitablefor allowing through water molecules in vapour form. This has theconsequence that on the discharge side of the membrane only waterbecomes available which has been in vapour phase, thus precluding thepresence of substances dissolved or otherwise present in the water.

According to yet another preferred embodiment the membrane is formedinto a number of substantially cylinder surface-shaped units, whereinthe axes of each of the cylinder surfaces extend mutually parallel, andwherein at least one end of the cylinders is connected to a collectingtank forming part of the discharge means.

It will be apparent that in a large-scale application of the presentinvention, where the object is of course to achieve sufficient wateroutput, the membrane will have to have as large a surface area aspossible. It has been found that with the above stated measures a largesurface area of the membrane can be realized within a relatively smallvolume, but wherein the dimensioning has yet to be determined. This inany case depends on the properties of the membrane, the thicknessthereof, the flow rate of the gas from which the water must beextracted, pressures, temperatures and so on.

It is also possible in principle to apply other configurations of themembrane, such as a membrane in the form of a plate, a spiral and so on.

According to a preferred embodiment the substantially cylindersurface-shaped units are manufactured from hollow tubes or fibres of themembrane or from capillaries.

The initial processing of the membrane material into tubes or fibresmakes it particularly possible to manufacture the above statedstructure.

Another preferred embodiment teaches that the substantially cylindersurface-shaped units are placed with a vertical axis in a substantiallyvertically extending flue gas duct.

The advantages of the above stated configurations are hereby combined.

It is otherwise also possible to fold the axis of the cylinder surfaceshorizontally.

When the apparatus is applied in a flue gas discharge duct of anincineration plant provided with a flue gas desulphurizing installationoperating with water, the apparatus is preferably placed downstream ofthe flue gas desulphurizing installation.

Flue gas desulphurizing installations generally operate with largequantities of water, a part of which remains in the flue gases saturatedwith water vapour to be further released to the atmosphere. It istherefore important to place the apparatus according to the inventiondownstream of the flue gas desulphurizing installation in order to alsoenable recovery of the water fed into the flue gas desulphurizinginstallation.

It is also possible for the cooling means to be adapted to maintain atemperature below the dew point of water in the collecting tank.

Another measure teaches that the means for maintaining a low temperatureon the second side of the membrane are adapted to make effective use ofthe heat released on the second side of the membrane. The efficiency ofan electric power station can hereby be improved slightly.

A further improvement in efficiency is possible in that the watercontent of the flue gases is decreased. The danger of condensationoccurring is also reduced. The need for additional heating of the fluegases before they are carried to the chimney in order to preventcondensation is hereby reduced.

An electric power plant not only produces water but also consumesconsiderable quantities of water as boiler feed water. The boiler feedwater comes for the greater part from the condenser, so that acirculation is obtained. The circulation is however not completelyclosed, since water loss does occur. This water loss can be easilycompensated with a apparatus according to the invention. A considerablesaving of potable water is obtained herewith, since the boiler make-upwater must be of high quality and pre-treated potable water or springwater, groundwater or surface water is normally used.

The present invention will now be further elucidated with reference tothe accompanying FIGURE, in which:

FIG. 1 shows a schematic view of a flue gas duct in which an embodimentaccording to the present invention is applied.

FIG. 2 shows a diagram of a power station into which the invention isintegrated.

FIG. 1 shows a flue gas duct 1 is shown which is provided with a widenedportion 2. The apparatus according to the present invention designatedin its entirety with 3 is arranged in widened portion 2. The widenedportion 2 serves to maintain a sufficient passage despite thearrangement of apparatus 3.

It is otherwise also possible to place the apparatus in a non-widenedflue gas duct; this applies particularly if the apparatus is placed inan existing chimney.

The actual apparatus is formed by a number of pipes 4 manufactures frommembrane material which are suspended in vertical direction from amanifold 5. The hoses are connected on their upper side to the inside ofmanifold 5 which is connected to a tank 8. On their underside the hosesare connected by means of a clamping ring 6 or other connection to amanifold 7 which is also connected to tank 8. Although manifolds 5, 7are only shown in one dimension, it will be apparent that they willgenerally take a two-dimensional form.

Connected to tank 8 is a discharge pipe 9 in which is arranged a valve10. Use is further made of a cooling device 11 which is already presentper se in a power station and the cooling spiral 12 of which extendsinto tank 8, and tank 8 is connected to a vacuum pump 13.

The operation of this apparatus will now be described.

As the flue gases move through duct 1, the water vapour present in theflue gases will pass through the membrane received in hoses 4. It thenenters the interior of hoses 4 and subsequently flows through manifold 7into tank 8. The tank can be drained as required by means of valve 10.

In order to enhance the transport through the membrane use is made of avacuum pump 13 which decreases the vacuum and thereby also the partialwater pressure inside tank 8.

To cool the contents of tank 8 use is made of a cooling device 11. Thisalso improves the transport through the membrane wall.

It will be apparent that the cooler according to the above embodiment isformed by a condenser of a device for converting chemical energy intomechanical energy. Other components can also form part of the normalinfrastructure of an electricity power station.

This possibility moreover provides the option of creating a circulatinggas flow, whereby the vapour pressure inside the hoses can be maintainedmore easily at a lower level. In this circulating gas flow use can bemade of a “sweep gas”, which is formed for instance, but notnecessarily, by nitrogen. The flushing gas reduces the concentration ofwater molecules on the rear side of the membrane, whereby the transportof water molecules is enhanced.

It is otherwise also possible to apply membranes in configurations otherthan tube or pipe-shaped configurations. It is thus possible forinstance to place the membranes in substantially flat planes. The flowof waste gases is preferably guided parallel along the plane so as tomake the contact time as long as possible. The membrane can further beprovided with ribs and folds in order to make the surface area as largeas possible. Numerous other configurations can also be envisaged.

The advantages of the invention are particularly manifest when thepreparation apparatus is integrated into an electrical power station.

The electrical power station comprises a boiler and a discharge duct forflue gases connecting thereto. A membrane is placed in this dischargeduct, which also includes the chimney, together with optional flue gasdesulphurizing installations. A membrane is understood to mean allconceivable combinations and configurations of membranes which aresuitable for the invention.

Boiler is further incorporated in a circuit for performing a Carnotcycle, which circuit is provided with a turbine, a condenser and a pump.A pump is arranged to maintain a sufficiently low pressure in thecondenser. Such a circuit is generally applied in electrical powerstations. According to the invention use can advantageously be made ofcondenser and vacuum pump. Both these elements are used to maintain thedesired conditions on the outlet side of the membrane. It is possiblealso, or alternatively, to apply other elements already present in theelectrical power station, such as pumps and the like.

Numerous other possibilities are also present by way of modification ofthis proposal. For instance by placing the cylinder surface-shapedbodies in a ring along the periphery of a flue gas duct.

Another field of application is in cooling towers such as are used inelectrical power stations. Water coming from the cooling circuit of thepower station is herein cooled before it is fed to the surface water.For this purpose the water for cooling is sprayed. A significant part ofthis sprayed water will evaporate. The evaporation energy originatesfrom the remaining water which will cool.

The water vapour rises inside the cooling tower and will exit to theatmosphere. This is a considerable quantity of water which—normally—islost for further effective use.

By placing a apparatus according to the invention in the cooling towerat least a significant part of the evaporated water can be recovered andbe used for effective purposes.

In question here are enormous quantities of water which, using theapparatus according to the invention, become available without use ofenergy. Opposed to this there is of course the investment required forthe invention.

In the application in question use can be made of a configuration as isapplied in the case of flue gas ducts, albeit with a much largerdiameter, although it is also possible to make use of otherconfigurations.

Use can also be made here of the components present in theinfrastructure of an electrical power station, such as a condenser and avacuum pump for generating conditions for enhancing operation of themembrane.

In addition, the application of the above stated principle is alsodeemed possible on a smaller scale, for instance in dwellings. It isherein possible to make use of decentralized generation of energy, forinstance in warm countries with little water. Use is usually made hereinof air-conditioning systems wherein energy conversion is necessary.Heating systems can also make fruitful use of such an apparatusaccording to the invention.

The invention is otherwise not limited to the above describedapplications; it can for instance also be applied in the chemicalindustry and the processing industry; the presence of a conversiondevice with external combustion and the presence of flows ofwater-containing gases are important.

What is claimed is:
 1. A preparation apparatus for preparing water fromwater-containing gases wherein said gases are released from a conversiondevice with external combustion for converting chemical energy intomechanical energy, and wherein the conversion device comprises acondenser and a pump for maintaining pressure inside the condenser whichis lower than the ambient pressure, said apparatus comprising: at leastone membrane which is adapted to at least partly allow passage of watermolecules and substantially prevent passage of other molecules; guidingmeans for guiding the water-containing gases along a first side of themembrane; and discharge means arranged on the second side of themembrane for discharging the water released on the second side of themembrane, wherein, the apparatus is used for preparing water fromwater-containing gases released from said conversion device, and thedischarge means include the condenser and the pump.
 2. An apparatus asclaimed in claim 1, characterized in that the preparation apparatus isused for preparing water from water-containing gases released by a powerstation.
 3. An apparatus as claimed in claim 1, characterized in thatthe membrane is only suitable for allowing the passage of watermolecules in vapour form.
 4. An apparatus as claimed in claim 2,characterized in that a flue gas desulphurizing installation operatingwith water is located in the guiding means and that the apparatus islocated downstream from the flue gas desulphurizing installation.
 5. Anapparatus as claimed in claim 1, characterized in that the installationis placed in a cooling tower of an electric power station.
 6. Anapparatus as claimed in claim 5, characterized in that the apparatus isplaced directly above a spraying device present in the cooling tower. 7.An apparatus as claimed in claim 2, characterized in that the membraneis only suitable for allowing the passage of water molecules in vapourform.